Light-emitting diodes (LEDs) often can provide light in a more efficient manner than an incandescent light source and/or a fluorescent light source. LEDs are often used in connection with wavelength-converting materials (e.g., luminescent materials) which absorb light emitted by the LED and emit light having a different wavelength. As a result, wavelength-converting materials may enable light generation at wavelengths that otherwise would not be possible in LED-based systems without such materials.
Certain conventional techniques involve positioning wavelength-converting materials directly on top of the LED die. In some cases, such positioning can lead to a number of drawbacks (e.g., light back-scattering loss and thermal problems) which can negatively impact performance of the LED. For example, light back-scattering loss reduces light extraction and can generate heat within the LED that can lead to higher junction temperatures. The heat may be accumulated in the wavelength-converting material causing thermal degradation and also can reduce luminescent quantum efficiency.
Other conventional techniques have involved positioning the wavelength-converting material away from the LED die at a certain distance separated by an air gap to form a cavity. However, such techniques still may suffer from the loss of light re-entering the LED die and the wavelength-converting material may suffer significant heating issues which can lead to thermal degradation. The air cavity may also increase the light source etendue, which will reduce the light coupling efficiency.
Accordingly, improved light emitting systems and methods that use wavelength-converting material are needed.